In radio communication systems such as wireless local area networks (LANs), the feasibility of using a MIMO, which increases the transmission rate by using a plurality of transmitting parts and a plurality of receiving parts in transmitting and receiving data, is under study. The wireless LAN standard currently in the process of standardization (IEEE802.11n) is expected to use a MIMO. An example of radio communication system is disclosed in the Japanese Patent Laid-open No. 2002-44051.